LoadBalancer.java

biz/hammurapi/util/LoadBalancer.java

Violations

Inspector	Message	Severity	Location
Java Inspector 048	Copyrights information should be present in each file.	1
Java Inspector 089	Undocumented method	2	68:17
Java Inspector 089	Undocumented method	2	90:9
Java Inspector 089	Undocumented method	2	105:9
Java Inspector 026	Avoid hardwired string literals. Allowed literals: []	3	62:68

Source code

1/*
2 * hgcommons 9
3 * Hammurapi Group Common Library
4 * Copyright (C) 2003  Hammurapi Group
5 *
6 * This program is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU Lesser General Public
8 * License as published by the Free Software Foundation; either
9 * version 2 of the License, or (at your option) any later version.
10 *
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
14 * Lesser General Public License for more details.
15 *
16 * You should have received a copy of the GNU Lesser General Public
17 * License along with this library; if not, write to the Free Software
18 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
19 *
20 * URL: http://www.hammurapi.biz/hammurapi-biz/ef/xmenu/hammurapi-group/products/products/hgcommons/index.html
21 * e-Mail: support@hammurapi.biz
22 */
23package biz.hammurapi.util;
24
25import java.util.ArrayList;
26import java.util.Collections;
27import java.util.Iterator;
28import java.util.List;
29
30/**
31 * Load balancer distributes work to other workers
32 * according to weights. The less the weight the more
33 * job worker is getting.
34 * @author Pavel Vlasov
35 * @revision $Revision$
36 */
37public class LoadBalancer implements Worker {
38
39	private List workers=new ArrayList();
40	
41	private void descore() {
42		synchronized (workers) {
43			Iterator it=workers.iterator();
44			while (it.hasNext()) {
45				((WorkerEntry) it.next()).score-=Integer.MAX_VALUE;
46			}
47		}
48	}
49	
50	private class WorkerEntry implements Comparable {
51		Worker worker;
52		int weight;
53		int score;
54		
55		/**
56		 * @param worker
57		 * @param weight Must be >0
58		 */
59		WorkerEntry(Worker worker, int weight) {
60			super();
61			if (weight<1) {
62				throw new IllegalArgumentException("Worker weight must be >0");
63			}
64			this.worker = worker;
65			this.weight = weight;
66		}
67
68		public int compareTo(Object o) {
69			if (o instanceof WorkerEntry) {
70				return score-((WorkerEntry) o).score;
71			}
72				
73			return hashCode()-o.hashCode();
74		}
75		
76		boolean post(Runnable job) {
77			if (worker.post(job)) {
78				// reduce all scores to avoid overflow.

79				if (score>Integer.MAX_VALUE-weight) {
80					descore();
81				}
82				
83				score+=weight;
84				return true;
85			}
86			return false;
87		}
88	}
89	
90	public boolean post(Runnable job) {
91		synchronized (workers) {
92			Collections.sort(workers);
93			Iterator it=workers.iterator();
94			while (it.hasNext()) {
95				WorkerEntry we=(WorkerEntry) it.next();
96				if (we.post(job)) {
97					return true;
98				}
99			}
100		}
101		
102		return false;
103	}
104
105	public void addWorker(Worker worker, int weight) {
106		synchronized (workers) {
107			workers.add(new WorkerEntry(worker, weight));
108		}
109	}
110}
111